P2128: Accelerator pedal sensor 2 exceeds its electrical upper limit

P2128 identifies a high APP2 signal in the reviewed GM diagnostic table. The generic dictionary calls this sensor E, but this particular monitor belongs to the second accelerator pedal position channel.

Why the upper limit is below full reference voltage

The threshold is greater than 52% of the reference scale, with 100% defined as five volts. That is an electrical scale, not a statement that using more than half the pedal travel is abnormal. APP2 has a different expected range from APP1, so applying the first channel's upper limit would miss the intended diagnosis.

The monitor requires run/crank voltage above 6.41 V and excludes an associated reference fault named P0697. The row's reference-number wording is inconsistent; it should not be used as a wiring-identification guide.

Capture the signal, not just the code

The strategy detects both continuous and intermittent short-high behavior. Its count windows allow 19 failures in 39 counts or 14 consecutive failures, evaluated at 12.5-millisecond intervals. This explains why a later stationary reading can look normal even when the recorded event was meaningful.

Interpret APP2 together with supply and reference status. A high signal establishes what the controller observed, but does not distinguish a circuit fault from an internal sensor problem by itself. Verification needs stable, plausible APP2 behavior under the applicable service test and a completed monitor without recurrence. The source specifies Type A, one-trip behavior, without documenting a particular replacement part.

Source and applicability

This explanation is limited to the documented 2025 GM monitor; its thresholds are not universal vehicle specifications. GM diagnostic table, PDF page 600.